Modeling the role of the close‐range effect and environmental variables in the occurrence and spread of P hragmites australis in four sites on the F innish coast of the G ulf of F inland and the A rchipelago S ea

P hragmites australis , a native helophyte in coastal areas of the B altic S ea, has significantly spread on the Finnish coast in the last decades raising ecological questions and social interest and concern due to the important role it plays in the ecosystem dynamics of shallow coastal areas. Despite its important implications on the planning and management of the area, predictive modeling of P hragmites distribution is not well studied. We examined the prevalence and progression of P hragmites in four sites along the Southern Finnish coast in multiple time frames in relation to a number of predictors. We also analyzed patterns of neighborhood effect on the expansion and disappearance of P hragmites in a cellular data model. We developed boosted regression trees models to predict P hragmites occurrences and produce maps of habitat suitability. Various P hragmites spread figures were observed in different areas and time periods, with a minimum annual expansion rate of 1% and a maximum of 8%. The water depth, shore openness, and proximity to river mouths were found influential in P hragmites distribution. The neighborhood configuration partially explained the dynamics of P hragmites colonies. The boosted regression trees method was successfully used to interpolate and extrapolate P hragmites distributions in the study sites highlighting its potential for assessing habitat suitability for P hragmites along the Finnish coast. Our findings are useful for a number of applications. With variables easily available, delineation of areas susceptible for P hragmites colonization allows early management plans to be made. Given the influence of reed beds on the littoral species and ecosystem, these results can be useful for the ecological studies of coastal areas. We provide estimates of habitat suitability and quantification of P hragmites expansion in a form suitable for dynamic modeling, which would be useful for predicting future P hragmites distribution under different scenarios of land cover change and P hragmites spatial configuration.